Combination fire tube and water tube boiler

ABSTRACT

Fire tube and water tube boilers are mounted on opposite sides of one upright wall of a casing and connected to common mud and steam drums. The drums are communicated by downcomers which, together with fire tube boilers, are confined in a dead air space within the casing. The water tube boiler is mounted in an upright position in a gas pass on the exterior of the casing at one side thereof.

United States Patent (56] References Cited UNITED STATES PATENTS 2 943 Stallbaum.,..........v..

(72I Inventor DenkGCsathy Minneapolis, Minn. 14.432

{21] AppLNo. I22] Filed Feb. 26, I970 Patented July 6, I971 [73] Assignee lhy Go, In.

FOREIGN PATENTS 5/1924 GreatBritain................

Primary Examiner- Kenneth W. Sprague n Jones Minneapolis, Minn.

Attorney-Ira Milto (54] COMBINATION FIRE TUBE AND WATER TUBE Bolum ABSTRACT: Fire tube and water tube boilers are men nted on n e ne oru. a s

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122/7, 42, tube boiler is mounted in an upright position in a gas pass on 43 the exterior of the casing at one side thereof.

PATENTEDJUL BIB?) 3.690 785 SHEET 1 BF 2 FIGJ.

INVENTOR Dams G. Usathy ATTORN Y This invention relates to boilers, and it has more particular reference to improvements in combination fire tube and water tube boilers of the type disclosed in my U.S. Pat. No. 3,246,633, issued Apr. 19, 1966.

Combination fire tube and water tube boilers are particularly well adapted for some processes of the petrochemical industry such as the production of hydrogen, ammonia and methanol by steam-methane reforming. In these processes the process gas that issues from the reformer furnace must be significantly cooled before it can be further processed. Thus at one stage in these processes, two separate streams of high temperature gas issue from the reformer furnace. One is the process gas itself, which is a relatively high pressure, and the other is the flue gas from the combustion chamber of the reformer furnace, which flue gas leaves the furnace at near atmospheric pressure.

Since steam is needed in the process it is obviously economically advantageous to use the heat that must be abstracted from the process gas and the heat contained in the flue gas to produce steam. For the high pressure process gas, this is best done in a fire tube boiler, but for most efficient recovery of heat from the flue gas, a water tube boiler should be used.

Prior to the development of the combination fire tube and water tube boiler of my aforesaid U.S. Pat. No. 3,246,633 This was done by two entirely separate boilers. Combining the tire tube and water tube boilers as in said patent effected a substantial economy. Not only was the costly duplication of much of the boiler structure such as casing walls, the external trim and controls eliminated, but also a saving in space requirements was effected.

However, the combination fire tube and water tube boiler of my aforesaid patent was found to have certain objectional features. Because its fire tube section inherently served as a mud drum, accumulation of "mud" therein could and did result in overheating of some of the fire tubes. As a consequence, these tubes would burn out. Replacement of the damaged tubes was not only a time consuming and costly operation, but it also disrupted the gas producing process.

SUMMARY OF THE INVENTION With the foregoing in mind, it is the purpose of this invention to provide a combination fire tube and water tube boiler having one or more fire tube boilers feeding a common steam drum and having a common mud drum which is entirely separate from these boilers but connected thereto by risers, and with the steam drum by downcomers. An important characteristic of this arrangement is that because the fire tube boilers are separate from the mud drum, they can be mounted at levels above that of the mud drum to thus assure against burn out" of the fire tubes by the inevitable accumulations of mud.

Another and equally important feature of the invention resides in the way in which the two boiler sections are combined. In accordance with the invention the tire tube boiler or boilers are at one side of the downcomers in a dead air space or compartment, .and a gas pass containing a bank of water tubes is at the other side of the downcomers.

With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings, which exemplify the invention, it being understood that such changes in the specific apparatus disclosed herein may be made as come within the scope of the appended claims.

The accompanying drawings illustrate one complete example of the embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

FIG. I is a more or less diagrammatic cross-sectional view through a combination fire tube and water tube boiler embodying this invention; and

FIG. 2 is a side view thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the accompanying drawings, the numeral 5 designates generally the fire tube section and the numeral 6 the water tube section of a combination boiler constructed in accordance with this invention.

The fire tube section 5 comprises a steam drum 7, a mud drum 8 and two fire tube boilers 9 and ID. All of these units are arranged horizontally with the steam drum at the top, the mud drum at the bottom and the two fire tube boilers therebetween. A number of downcomer tubes I I extend vertically between the steam and mud drums and are secured thereto. These downcomer tubes not only serve to communicate the interiors of the drums so that the mud drum receives water from the steam drum, but they also structurally support the steam drum. The downcomers are preferably disposed with their axes lying in the same vertical plane that contains the axes of the steam and mud drums.

The steam and mud drums are also connected with the superimposed fire tube boilers by groups of risers l2, l3 and M, which like the downcomers ll structurally tie the drums and boilers together and communicate them one with the other. The fire tube boilers are thus series connected with the mud and steam drums to provide for natural circulation of boiler fluid from one to the other.

Each of the fire tube boilers consists of an elongated drum or shell IS with a plurality of fire tubes [6 therein connecting gas inlet and outlet manifolds l7 and 18, respectively, at the opposite ends of the drum or shell. The risers, of course, communicate the interiors of the drums or shells of the two fire tube boilers with one another and with the steam and mud drums.

The lower boiler II], which is somewhat larger in diameter than the upper boiler 9, is disposed at a level slightly above that of the mud drum. This arrangement enables the precipitant impurities contained in the feed water to settle and accumulate in the mud drum and not in the lower fire tube boiler 10. By way of example, the bottom of the lower fire tube boiler can be at about the same level as the top of the mud drum, as shown, to insure mud-free operation of the fire tube boilers.

As seen in FIG. 2, the gas inlet I? of the upper fire tube boiler 9 is at the left hand end thereof, while the lower fire tube boiler 10 has its gas inlet at its opposite or right-hand end. High-pressure process gas to be cooled enters the boilers through their inlets and flows through the fire tubes I6 in indirect heat transfer relation to the boiler fluid circulating through the drums or shells 15 of the boilers. Heat abstracted from the process gas is thus transferred to the boiler fluid to produce steam which accumulates in the steam drum, while the cooled process gas issues from the outlets 18 of the fire tube boilers.

As also seen best in FIG. 2, there are four downcomers ll connected between the steam and mud drums, two near each end thereof, in spaced apart relation to one another along the length of the drums. Also, there are six risers in each groups l2, l3 and 14, the endmost of which, lengthwise of the drums, are located transversely in line with the endmost downcomers.

Most of the steam generated in each of the fire tube boilers is formed in that end portion which is nearest its gas inlet l7; and since these inlets are remote from one another, the steam generated in the two fire tube boilers enters the steam drum mainly at the end portions thereof.

The steam generated in the water tube boiler 6 is preferably delivered into the steam drum at its midsection. Hence, the three boilers discharge steam into different but axially adjacent zones in the steam drum, rather than all at one zone, and, as a result, quieter operation is obtained.

The water tube boiler 6 comprises a bank of generally vertical water tubes 20 housed in a flue gas pass 21 and having their ends connected to the steam and mud drums. The gas pass is defined in part by one of the walls 22 of a casing 23 that forms a dead air space in which the fire tube boiler section is located.

The wall 22 is preferably closely adjacent to, but exteriorly of, the downcomers, and hence lies between the downcomers and the bank of water tubes 20.

Cooperating with the wall 22 to define the casing 23 are a sidewall 24, end walls 25, and a bottom wall 26. The steam and mud drums also contribute in the formation of the casing 23. Since this casing merely encloses a dead air space, its external walls need not be heavily insulated, but preferably have some insulation on their inner surfaces, as shown. Inasmuch as the water tube boiler section extends for only part of the length of the fire tube boiler section, only the middle portion of the wall 22 is common to the flue gas pass. The flue gas pass is completed by a sidewall 27 and end walls 28, and openings 29 and 30in the upper and lower ends of the flue gas pass provide for flow of flue gases into and from said pass. All of the walls of the gas pass are appropriately insulated, but inasmuch as the several drums are structurally connected by the downcomers, the risers and the bank of water tubes, neither the walls of the casing 23 nor of the gas pass 21 need be load bearing.

During operation, natural circulation of boiler fluid takes place through the water tubes as well as through the fire tube boilers 9 and 10. Accordingly the steam generating plant of this invention is ideally suited for the utilization of heat from two different sources, as for example the process gas which in hydrogen, ammonia and methanol producing plants must be cooled and the combustion or flue gas which leaves the combustion chamber of the processing furnace.

However, the invention is not limited to use with gas producing plants, as it will function efficiently in the generation of steam regardless of the nature or source of the hot gases circulated through the fire tube and water tube boiler sections which comprise the steam generating plant, providing that the hot gases which pass through the gas pass of the water tube boiler are not at too high a pressure.

It will also be appreciated that if desired, the tubes 20 of the water tube boiler can be provided with extended surface, such as fins or the like to improve their ability to abstract heat from the hot gases flowing over them. In fact, it may be desirable in some instances to employ in the gas pass 21 a water tube boiler and baffle arrangement such as that disclosed in my copending application Ser. No. 882,l96, filed Dec. 4, I969, wherein the tubes are provided with extended surface.

From the foregoing description, together with the accompanying drawings, it will be readily apparent to those skilled in the art that this invention provides an efficient steam generating plant featuring an improved arrangement of fire tube and water tube boilers and steam and mud drums associated therewith.

Those skilled in the art will appreciate that the invention can be embodied in forms other than as herein disclosed for purposes of illustration.

The invention is defined by the following claims.

lclaim:

l. A combination fire tube and water tube boiler comprisin z a. a substantially horizontal steam drum;

B. a substantially horizontal mud drum beneath the steam drum;

C. substantially vertical downcomer means connecting said drums;

D. a fire tube boiler between the steam and mud drums at one side of said downcomer means,

said fire tube boiler having a drum and fire tubes extending through said drum between inlet and outlet means at the opposite ends of the drum;

E. riser means connecting the drum of the fire tube boiler with the steam and mud drums,

said riser means and downcomer means together with said drums providing a first natural circulation path for a recipient fluid medium to and from the steam drum; D. wall means defining a gas pass at the other side of said downcomer means, said gas pass having inlet and outlet means; 0. and a bank of water tubes in said gas pass having their ends connected with the steam and mud drums, said bank of water tubes together with the downcomer means and said drums providing a second natural circulation path for the recipient fluid medium to and from the steam drum,

said two natural circulation paths enabling the abstraction of heat simultaneously from a hot gaseous high pressure donor medium circulated through the tubes of the fire tube boiler and from a hot gaseous low pressure donor medium circulated through said gas pass.

2. The combination fire tube and water tube boiler of claim 1, further characterized by a second fire tube boiler between the steam and mud drums and also connected therewith to provide for natural circulation of the recipient fluid medium to and from the steam drum in indirect heat transfer relation with hot gaseous high pressure donor medium circulated through its fire tubes,

and further characterized in that the drums of the fire tube boilers are substantially coextensive in length with the steam and mud drums;

at least certain of said riser means which communicate the drums of the fire tube boilers with the steam and mud drums being located near the ends of the drums; and

the donor medium inlet means of the two fire tube boilers being at the opposite ends thereofso that the hot gaseous donor medium flows in opposite directions through the two fire tube boilers.

3. The combination fire tube and water tube boiler ofclaim 2, wherein the connections of all of the water tubes with the steam drum are confined to a zone spaced appreciably from the ends of the steam drum 4. A combination fire tube and water tube boiler, characterized by:

A. wall members defining an upright elongated casing;

B steam and mud drums extending lengthwise along the top and bottom, respectively of the casing;

C. downcomers connecting said drums;

D. a fire tube boiler extending lengthwise through the casing at a level considerably above the bottom of the mud drum;

E. risers connecting the fire tube boiler in series with the mud and steam drums;

F. wall means defining a gas pass on one side of the casing at its exterior;

G. and a water tube boiler in the gas pass, also connected with the mud and steam drums.

5. The combination fire tube and water tube boiler of claim wherein one of said wall members of the casing also forms part of the wall means defining the gas pass.

6. The combination fire tube and water tube boiler of claim wherein said fire tube boiler is positioned between the downcomers and a wall member of the casing which is opposite said one wall member, and wherein said one wall member occupies a position intermediate the downcomers and the water tube boiler.

7. The combination fire tube and water tube boiler of claim 4, further characterized by:

A. a second fire tube boiler extending lengthwise through the casing and spaced above the first designated fire tube boiler, both of said fire tube boilers being substantially coextensive in length with the steam and mud drums;

B. a heating medium inlet for each fire tube boiler, said inlets being located at the opposite end portions of the boilers; and

C. said risers connecting both fire tube boilers with the mud and steam drums.

8. The combination fire tube and water tube boiler of claim 7, wherein the heating medium inlets are at the remote ends of the fire tube boilers,

so that most of the steam generated in the fire tube boilers ascends to the steam drum through risers which are located at the opposite end portions of the fire tube boilers, and wherein the connection of the water tube boiler with the steam drum is confined to a zone spaced appreciably from the ends of the steam drum.

9. The combination fire tube and water tube boiler of claim 4, further characterized by:

A. said fire tube boiler having an inlet for a heating medium at one end thereof;

B. one of said risers being connected with the fire tube boiler at a location adjacent to the inlet end thereof and with the steam drum at its end portion which is directly above said inlet end of the boiler; and

C. the water tube boiler being connected with the steam drum at a location spaced a distance from said end portion thereof toward the opposite end of the steam drum.

10. The combination fire tube and water tube boiler of claim 4, further characterized by:

A. said gas pass having openings at the top and bottom thereof to provide for circulation of hot gases therethrough; and

B. said casing providing a dead air space in which the fire tube boiler, the risers connecting therewith and the downcomers are located.

II. A combination boiler having a steam drum connected with a fire tube boiler and with a water tube boiler to receive steam therefrom, characterized by:

A. a mud drum having connections with the fire tube and water tube boilers;

B. downcomers connecting the steam drum with the mud drum;

C. the tire tube boiler being connected by risers with said drums; and

D. wall means providing 1. a compartment in which the fire tube boiler is con- 2. and a gas pass separate from but at one external side of said compartment, in which the water tube boiler is mounted.

I2. The combination boiler of claim 11, wherein the fire tube boiler is at a level at least partially above that of the mud drum.

13. The combination boiler of claim ll, wherein the downcomers are also located in said compartment with the fire tube boiler. 

1. A combination fire tube and water tube boiler comprising: A. a substantially horizontal steam drum; B. a substantially horizontal mud drum beneath the steam drum; C. substantially vertical downcomer means connecting said drums; D. a fire tube boiler between the steam and mud drums at one side of said downcomer means, said fire tube boiler having a drum and fire tubes extending through said drum between inlet and outlet means at the opposite ends of the drum; E. riser means connecting the drum of the fire tube boiler with the steam and mud drums, said riser means and downcomer means together with said drums providing a first natural circulation path for a recipient fluid medium to and from the steam drum; D. wall means defining a gas pass at the other side of said downcomer means, said gas pass having inlet and outlet means; G. and a bank of water tubes in said gas pass having their ends connected with the steam and mud drums, said bank of water tubes together with the downcomer means and said drums providing a second natural circulation path for the recipient fluid medium to and from the steam drum, said two natural circulation paths enabling the abstraction of heat simultaneously from a hot gaseous high pressure donor medium circulated through the tubes of the fire tube boiler and from a hot gaseous low pressure donor medium circulated through said gas pass.
 2. The combination fire tube and water tube boiler of claim 1, further characterized by a second fire tube boiler between the steam and mud drums and also connected therewith to provide for natural circulation of the recipient fluid medium to and from the steam drum in indirect heat transfer relation with hot gaseous high pressure donor medium circulated through its fire tubes, and further characterized in that the drums of the fire tube boilers are substantially coextensive in length with the steam and mud drums; at least certain of said riser means which communicate the drums of the fire tube boilers with the steam and mud drums being located near the ends of the drums; and the donor medium inlet means of the two fire tube boilers being at the opposite ends thereof so that the hot gaseous donor medium flows in opposite directions through the two fire tube boilers.
 2. and a gas pass separate from but at one external side of said compartment, in which the water tube boiler is mounted.
 3. The combination fire tube and water tube boiler of claim 2, wherein the connections of all of the water tubes with the steam drum are confined to a zone spaced appreciably from the ends of the steam drum.
 4. A combination fire tube and water tube boiler, characterized by: A. wall members defining an upright elongated casing; B. steam and mud drums extending lengthwise along the top and bottom, respectively of the casing; C. downcomers connecting said drums; D. a fire tube boiler extending lengthwise through the casing at a level considerably above the bottom of the mud drum; E. risers connecting the fire tube boiler in series with the mud and steam drums; F. wall means defining a gas pass on one side of the casing at its exterior; G. and a water tube boiler in the gas pass, also connected with the mud and steam drums.
 5. The combination fire tube and water tube boiler of claim 4, wherein one of said wall members of the casing also forms part of the wall means defining the gas pass.
 6. The combination fire tube and water tube boiler of claim 5, wherein said fire tube boiler is positioned between the downcomers and a wall member of the casing which is opposite said one wall member, and wherein said one wall member occupies a position intermediate the downcomers and the water tube boiler.
 7. The combination fire tube and water tube boiler of claim 4, further characterized by: A. a second fire tube boiler extending lengthwise through the casing and spaced above the first designated fire tube boiler, both of said fire tube boilers being substaNtially coextensive in length with the steam and mud drums; B. a heating medium inlet for each fire tube boiler, said inlets being located at the opposite end portions of the boilers; and C. said risers connecting both fire tube boilers with the mud and steam drums.
 8. The combination fire tube and water tube boiler of claim 7, wherein the heating medium inlets are at the remote ends of the fire tube boilers, so that most of the steam generated in the fire tube boilers ascends to the steam drum through risers which are located at the opposite end portions of the fire tube boilers, and wherein the connection of the water tube boiler with the steam drum is confined to a zone spaced appreciably from the ends of the steam drum.
 9. The combination fire tube and water tube boiler of claim 4, further characterized by: A. said fire tube boiler having an inlet for a heating medium at one end thereof; B. one of said risers being connected with the fire tube boiler at a location adjacent to the inlet end thereof and with the steam drum at its end portion which is directly above said inlet end of the boiler; and C. the water tube boiler being connected with the steam drum at a location spaced a distance from said end portion thereof toward the opposite end of the steam drum.
 10. The combination fire tube and water tube boiler of claim 4, further characterized by: A. said gas pass having openings at the top and bottom thereof to provide for circulation of hot gases therethrough; and B. said casing providing a dead air space in which the fire tube boiler, the risers connecting therewith and the downcomers are located.
 11. A combination boiler having a steam drum connected with a fire tube boiler and with a water tube boiler to receive steam therefrom, characterized by: A. a mud drum having connections with the fire tube and water tube boilers; B. downcomers connecting the steam drum with the mud drum; C. the fire tube boiler being connected by risers with said drums; and D. wall means providing
 12. The combination boiler of claim 11, wherein the fire tube boiler is at a level at least partially above that of the mud drum.
 13. The combination boiler of claim 11, wherein the downcomers are also located in said compartment with the fire tube boiler. 